STRUCTURE OF TiO2 SURFACES AND THEIR INTERFACES WITH WATER A. Selloni - Dept. of Chemistry, Princeton University Titanium dioxide is a widely used material with a large variety of applications, in heterogeneous catalysis, as a photocatalyst, in solar cells, etc. The importance of these applications has motivated a great interest in the surface properties of this material, and indeed TiO2 is the most investigated single-crystalline system in the surface science of metal oxides. In this talk, we shall discuss the structure and stability of TiO2 surfaces and their interfaces with water on the basis ab initio molecular dynamics simulations. Results for both the case of stoichiometric and reduced surfaces will be presented, showing the critical role of surface defects in the reactivity properties.